Today, with the increased emphasis on products liability and reliability, there is a greater need than ever before to identify machine parts and other components. Typically, a part is marked to indicate its origin, to aid in identifying a replacement, or to indicate its position or location within a major component or sub-assembly. The basic method for marking parts, and in particular hollow objects such as nuts, spark plugs, collars, bushings and the like, involves the use of a stud arbor. In that method, the part that is to be marked is manually positioned on a stud arbor. When the stud arbor is activated, the part is forced to come into contact with a marking die. The die, being of harder material than the object to be marked, impresses one or more characters on the exterior surface of the part. The part is then manually removed from the stud arbor. Other objects to be identified are similarly manually located, marked and removed.
One manual machine that has received wide acceptance in the industry is one manufactured by the George T. Schmidt Company. These manual machines are ordinarily provided with accessories for roll marking large cylindrical parts, springs return mechanisms to return the marking die to the same location after each marking cycle, and keys or jigs to insure that the object to be marked is marked at the same location on the part each time. It should be appreciated that any machine or mechanism relying upon manual steps or the intervention of a human operative is inherently slow. On the other hand, such machines are especially useful in those industrial processes where only a relatively few parts must be marked or where the individual parts require special attention or alignment on a stud arbor. For example, the bezel on a camera lens is a part commonly marked with a manually operated stud arbor.
In order to speed production, a marking machine having an automatic reciprocating arbor was soon developed. Ordinarily, these machines are hydraulically operated and are synchronized with a chute containing a number of similar parts to be marked. In one device, a hydraulic cylinder operated a ratchet mechanism to actuate a revolving spider. The spider would carry the part under the marking die and hold it in such a manner that the object was free to rotate as the marking die was driven across its exterior surface. In some machines, the rotation of the stud arbor was synchronized with the marking die by a rack and pinion drive. Some machines employ a Geneva gear to rotate the spider, to eject the marked part and to receive an unmarked part from the supply chute. Typical speeds are from 2,000 to 3,000 parts marked per hour.
To further speed production, continuously moving, planetary machines were developed. In these machines, the stud arbor has time to become fully inserted within the hollow object while the machine is operating without the marking cycle being interrupted. In one planetary machine, each compartment of the planetary feed mechanism has its own reciprocating arbor. A concave lettering die is used to imprint characters on the parts. Hollow, round parts needing internal support, however, have to be manually placed on a support stud prior to marking. Speeds in excess of 3,000 pieces marked per hour have been achieved. The George T. Schmidt Co. Model 135 marking machine is a typical example. As can be appreciated, planetary marking machines are somewhat complex and, by necessity, require more than one arbor in order for such high rates of marking to be achieved. Planetary machines are limited in their versatility in that the separate compartments are unique or specifically related to the size of the object to be marked. Thus, interchangeability between different parts requiring marking is complicated and relatively expensive. In addition, such machines operate at one speed, the same speed being used to move the parts through the machine before, during, and after marking. Relatively speaking, a large portion of the marking time or cycle is devoted to moving the object relative to the time actually spent marking the object. In this sense, planetary machines are inefficient. A fast, efficient, versatile, simple-to-operate, and easy-to-maintain marking machine would be a welcome addition to the marketplace and would satisfy a long-felt, but heretofore unsatisified need by the industry for improved marking machines.